1. Field of the Invention
The present invention relates to a thermal interface material, and especially to a thermal interface material having carbon nano-capsules contained therein. The thermal interface material can be used for transferring heat away from a heat source to a heat sink or other heat dissipation device.
2. Description of Related Art
Recent advances in high speed semiconductor integrated circuit technology have resulted in semiconductor devices which are smaller and run faster than ever before. Such semiconductor devices also generate more heat than ever before. In order to ensure good performance and reliability of the semiconductor devices, their operational temperatures must be kept within a suitable range. Typically, a heat sink is attached to a surface of a semiconductor device, such as a central processing unit (CPU), so that heat is transferred from the semiconductor device to ambient air via the heat sink. When attaching the heat sink to the semiconductor device, respective surfaces of the device and heat sink are brought into intimate contact with each other. However, as much as 99% of the respective surfaces are separated from each other by a layer of interstitial air, no matter how precisely the heat sink and the semiconductor device are manufactured. Therefore, a thermal interface material is used to eliminate air gaps between the heat source and heat sink to improve heat flow.
Conventional thermal interface materials are thermally conductive compounds prepared by dispersing a plurality of thermally conductive fillers in a polymer matrix. The thermally conductive fillers can be graphite, boron nitride, silicon oxide, alumina, and so on. A typical thermal conductivity of the conventional thermal interface materials is only about 1 W/mK, since the polymer matrix has poor thermal conductivity. With the decreasing size and increasing speed of semiconductor devices, such as a CPU, heat dissipating requirements are increasing. To aid in solving the heat dissipation problem, an improved thermal interface material with a higher thermal conductivity is desired. One way to achieve this is to change the thermally conductive fillers in the polymer matrix. By doing this, an improvement of up to 4˜8 W/mK can be achieved. However, adding thermally conductive fillers into the polymer matrix helps only up to a point. If too many thermally conductive fillers are added, the polymer matrix loses its original performance. In particular, the polymer matrix can become stiffer and less flexible, and the soakage effect may be worsened. The thermally conductive characteristics of thermal interface materials have thus been limited for the above reasons.